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1 .so style
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2
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3 .TL
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4 .ps +4
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5 Why the Unix Philosophy still matters
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6 .AU
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7 markus schnalke <meillo@marmaro.de>
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8 .AB
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9 .ti \n(.iu
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10 This paper explains the importance of the Unix Philosophy for software design.
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11 Today, few software designers are aware of these concepts,
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12 and thus a lot of modern software is more limited than necessary
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13 and makes less use of software leverage than possible.
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14 Knowing and following the guidelines of the Unix Philosophy makes software more valuable.
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15 .AE
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16
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17 .FS
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18 .ps -1
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19 This paper was prepared for the ``Software Analysis'' seminar at University Ulm.
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20 Mentor was professor Franz Schweiggert.
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21 Handed in on 2010-04-12.
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22 You may retrieve this document from
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23 .CW \s-1http://marmaro.de/docs \ .
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24 .FE
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25
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26 .H 1 Introduction
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27 .LP
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28 The Unix Philosophy is the essence of how the Unix operating system,
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29 especially its toolchest, was designed.
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30 It is no limited set of fixed rules,
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31 but a loose set of guidelines which tell how to write software that
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32 suites well into Unix.
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33 Actually, the Unix Philosophy describes what is common to typical Unix software.
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34 The Wikipedia has an accurate definition:
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35 .[
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36 wikipedia
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37 unix philosophy
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38 .]
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39 .QP
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40 The \fIUnix philosophy\fP is a set of cultural norms and philosophical
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41 approaches to developing software based on the experience of leading
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42 developers of the Unix operating system.
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43 .PP
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44 As there is no single definition of the Unix Philosophy,
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45 several people have stated their view on what it comprises.
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46 Best known are:
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47 .IP \(bu
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48 Doug McIlroy's summary: ``Write programs that do one thing and do it well.''
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49 .[
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50 mahoney
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51 oral history
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52 .]
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53 .IP \(bu
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54 Mike Gancarz' book ``The UNIX Philosophy''.
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55 .[
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56 gancarz
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57 unix philosophy
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58 .]
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59 .IP \(bu
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60 Eric S. Raymond's book ``The Art of UNIX Programming''.
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61 .[
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62 raymond
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63 art of unix programming
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64 .]
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65 .LP
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66 These different views on the Unix Philosophy have much in common.
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67 Especially, the main concepts are similar in all of them.
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68 McIlroy's definition can surely be called the core of the Unix Philosophy,
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69 but the fundamental idea behind it all, is ``small is beautiful''.
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70
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71 .PP
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72 The Unix Philosophy explains how to design good software for Unix.
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73 Many concepts described here, base on facilities of Unix.
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74 Other operating systems may not offer such facilities,
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75 hence it may not be possible to design software in the way of the
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76 Unix Philosophy for them.
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77 .PP
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78 The Unix Philosophy has an idea of how the process of software development
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79 should look like, but large parts of the philosophy are quite independent
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80 from a concrete development process.
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81 However, one will soon recognize that some development processes work well
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82 with the ideas of the Unix Philosophy and support them, while others are
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83 at cross-purposes.
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84 Kent Beck's books about Extreme Programming are valuable supplemental
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85 resources on this topic.
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86 .PP
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87 The question of how to actually write code and how the code should looks
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88 like in detail, are out of focus here.
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89 ``The Practice of Programming'' by Kernighan and Pike,
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90 .[
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91 kernighan pike
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92 practice of programming
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93 .]
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94 is a good book that covers this topic.
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95 Its point of view matches to the one of this paper.
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96
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97 .H 1 "Importance of software design in general
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98 .LP
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99 Software design is the planning of how the internal structure
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100 and external interfaces of a software should look like.
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101 It has nothing to do with visual appearance.
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102 If we take a program as a car, then its color is of no matter.
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103 Its design would be the car's size, its shape, the locations of doors,
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104 the passenger/space ratio, the available controls and instruments,
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105 and so forth.
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106 .PP
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107 Why should software get designed at all?
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108 It is general knowledge, that even a bad plan is better than no plan.
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109 Not designing software means programming without plan.
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110 This will pretty sure lead to horrible results.
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111 Software that is horrible to use and horrible to maintain.
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112 These two aspects are the visible ones.
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113 Often invisible though, are the wasted possible gains.
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114 Good software design can make these gains available.
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115 .PP
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116 A software's design deals with quality properties.
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117 Good design leads to good quality, and quality is important.
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118 Any car may be able to drive from A to B,
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119 but it depends on the car's properties whether it is a good choice
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120 for passenger transport or not.
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121 It depends on its properties if it is a good choice
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122 for a rough mountain area.
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123 And it depends on its properties if the ride will be fun.
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124
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125 .PP
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126 Requirements for a software are twofold:
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127 functional and non-functional.
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128 .IP \(bu
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129 Functional requirements define directly the software's functions.
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130 They are the reason why software gets written.
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131 Someone has a problem and needs a tool to solve it.
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132 Being able to solve the problem is the main functional goal.
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133 It is the driving force behind all programming effort.
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134 Functional requirements are easier to define and to verify.
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135 .IP \(bu
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136 Non-functional requirements are called \fIquality\fP requirements, too.
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137 The quality of a software are the properties that are not directly related to
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138 the software's basic functions.
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139 Tools of bad quality often do solve the problems they were written for,
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140 but introduce problems and difficulties for usage and development, later on.
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141 Quality aspects are often overlooked at first sight,
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142 and are often difficult to define clearly and to verify.
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143 .PP
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144 Quality is hardly interesting when the software gets built initially,
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145 but it has a high impact on usability and maintenance of the software, later.
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146 A short-sighted might see in developing a software, mainly building something up.
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147 But experience shows, that building the software the first time is
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148 only a small amount of the overall work.
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149 Bug fixing, extending, rebuilding of parts \(en maintenance work \(en
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150 does soon take over the major part of the time spent on a software.
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151 And of course, the time spent actually using the software.
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152 These processes are highly influenced by the software's quality.
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153 Thus, quality must not be neglected.
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154 However, the problem with quality is that you hardly ``stumble over''
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155 bad quality during the first build,
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156 although this is the time when you should care about good quality most.
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157 .PP
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158 Software design has little to do with the basic function of a software \(en
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159 this requirement will get satisfied anyway.
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160 Software design is more about quality aspects of the software.
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161 Good design leads to good quality, bad design to bad quality.
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162 The primary functions of the software will be affected modestly by bad quality,
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163 but good quality can provide a lot of additional gain,
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164 even at places where one never expected it.
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165 .PP
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166 The ISO/IEC\|9126-1 standard, part\|1,
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167 .[
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168 iso product quality
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169 .]
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170 defines the quality model as consisting out of:
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171 .IP \(bu
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172 .I Functionality
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173 (suitability, accuracy, inter\%operability, security)
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174 .IP \(bu
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175 .I Reliability
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176 (maturity, fault tolerance, recoverability)
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177 .IP \(bu
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178 .I Usability
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179 (understandability, learnability, operability, attractiveness)
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180 .IP \(bu
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181 .I Efficiency
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182 (time behavior, resource utilization)
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183 .IP \(bu
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184 .I Maintainability
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185 (analyzability, changeability, stability, testability)
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186 .IP \(bu
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187 .I Portability
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188 (adaptability, installability, co-existence, replaceability)
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189 .LP
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190 Good design can improve these properties of a software,
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191 bad designed software likely suffers in these points.
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192 .PP
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193 One further goal of software design is consistency.
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194 Consistency eases understanding, working on, and using things.
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195 Consistent internal structure and consistent interfaces to the outside
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196 can be provided by good design.
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197 .PP
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198 Software should be well designed because good design avoids many
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199 problems during a software's lifetime.
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200 And software should be well designed because good design can offer
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201 much additional gain.
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202 Indeed, much effort should be spent into good design to make software more valuable.
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203 The Unix Philosophy shows a way of how to design software well.
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204 It offers guidelines to achieve good quality and high gain for the effort spent.
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205
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206
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207 .H 1 "The Unix Philosophy
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208 .LP
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209 The origins of the Unix Philosophy were already introduced.
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210 This chapter explains the philosophy, oriented on Gancarz,
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211 and shows concrete examples of its application.
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212
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213 .H 2 Pipes
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214 .LP
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215 Following are some examples to demonstrate how applied Unix Philosophy feels like.
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216 Knowledge of using the Unix shell is assumed.
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217 .PP
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218 Counting the number of files in the current directory:
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219 .DS
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220 ls | wc -l
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221 .DE
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222 The
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223 .CW ls
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224 command lists all files in the current directory, one per line,
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225 and
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226 .CW "wc -l
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227 counts the number of lines.
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228 .PP
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229 Counting the number of files that do not contain ``foo'' in their name:
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230 .DS
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231 ls | grep -v foo | wc -l
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232 .DE
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233 Here, the list of files is filtered by
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234 .CW grep
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235 to remove all lines that contain ``foo''.
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236 The rest equals the previous example.
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237 .PP
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238 Finding the five largest entries in the current directory.
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239 .DS
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240 du -s * | sort -nr | sed 5q
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241 .DE
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242 .CW "du -s *
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243 returns the recursively summed sizes of all files in the current directory
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244 \(en no matter if they are regular files or directories.
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245 .CW "sort -nr
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246 sorts the list numerically in reverse order (descending).
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247 Finally,
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248 .CW "sed 5q
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249 quits after it has printed the fifth line.
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250 .PP
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251 The presented command lines are examples of what Unix people would use
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252 to get the desired output.
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253 There are also other ways to get the same output.
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254 It's a user's decision which way to go.
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255 .PP
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256 The examples show that many tasks on a Unix system
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257 are accomplished by combining several small programs.
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258 The connection between the single programs is denoted by the pipe operator `|'.
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259 .PP
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260 Pipes, and their extensive and easy use, are one of the great
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261 achievements of the Unix system.
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262 Pipes between programs have been possible in earlier operating systems,
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263 but it has never been a so central part of the concept.
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264 When, in the early seventies, Doug McIlroy introduced pipes into the
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265 Unix system,
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266 ``it was this concept and notation for linking several programs together
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267 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
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268 .[
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269 aughenbaugh
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270 unix oral history
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271 .]
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272 .PP
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273 Being able to specify pipelines in an easy way is,
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274 however, not enough by itself.
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275 It is only one half.
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276 The other is the design of the programs that are used in the pipeline.
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277 They need interfaces that allow them to be used in such a way.
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278
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279 .H 2 "Interface design
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280 .LP
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281 Unix is, first of all, simple \(en Everything is a file.
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282 Files are sequences of bytes, without any special structure.
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283 Programs should be filters, which read a stream of bytes from standard input (stdin)
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284 and write a stream of bytes to standard output (stdout).
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285 If the files \fIare\fP sequences of bytes,
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286 and the programs \fIare\fP filters on byte streams,
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287 then there is exactly one data interface.
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288 Hence it is possible to combine programs in any desired way.
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289 .PP
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290 Even a handful of small programs yields a large set of combinations,
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291 and thus a large set of different functions.
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292 This is leverage!
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293 If the programs are orthogonal to each other \(en the best case \(en
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294 then the set of different functions is greatest.
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295 .PP
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296 Programs can also have a separate control interface,
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297 besides their data interface.
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298 The control interface is often called ``user interface'',
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299 because it is usually designed to be used by humans.
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300 The Unix Philosophy discourages to assume the user to be human.
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301 Interactive use of software is slow use of software,
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302 because the program waits for user input most of the time.
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303 Interactive software requires the user to be in front of the computer.
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304 Interactive software occupy the user's attention while they are running.
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305 .PP
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306 Now to come back to the idea of combining several small programs,
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307 to have a more specific function.
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308 If these single tools would all be interactive,
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309 how would the user control them?
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310 It is not only a problem to control several programs at once,
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311 if they run at the same time,
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312 it also very inefficient to have to control each of the single programs
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313 that are intended to act as one large program.
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314 Hence, the Unix Philosophy discourages programs to demand interactive use.
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meillo@11
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315 The behavior of programs should be defined at invocation.
|
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meillo@45
|
316 This is done by specifying arguments to the program call
|
|
meillo@45
|
317 (command line switches).
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|
meillo@11
|
318 Gancarz discusses this topic as ``avoid captive user interfaces''.
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meillo@46
|
319 .[ [
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|
meillo@44
|
320 gancarz unix philosophy
|
|
meillo@46
|
321 .], page 88 ff.]
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meillo@11
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322 .PP
|
|
meillo@11
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323 Non-interactive use is, during development, also an advantage for testing.
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meillo@11
|
324 Testing of interactive programs is much more complicated,
|
|
meillo@11
|
325 than testing of non-interactive programs.
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meillo@5
|
326
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meillo@48
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327 .H 2 "The toolchest approach
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|
meillo@5
|
328 .LP
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meillo@5
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329 A toolchest is a set of tools.
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meillo@5
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330 Instead of having one big tool for all tasks, one has many small tools,
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meillo@5
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331 each for one task.
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meillo@5
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332 Difficult tasks are solved by combining several of the small, simple tools.
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meillo@5
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333 .PP
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|
meillo@11
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334 The Unix toolchest \fIis\fP a set of small, (mostly) non-interactive programs
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|
meillo@11
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335 that are filters on byte streams.
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meillo@11
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336 They are, to a large extend, unrelated in their function.
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meillo@11
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337 Hence, the Unix toolchest provides a large set of functions
|
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meillo@11
|
338 that can be accessed by combining the programs in the desired way.
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meillo@11
|
339 .PP
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meillo@11
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340 There are also advantages for developing small toolchest programs.
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meillo@5
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341 It is easier and less error-prone to write small programs.
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meillo@5
|
342 It is also easier and less error-prone to write a large set of small programs,
|
|
meillo@5
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343 than to write one large program with all the functionality included.
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meillo@5
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344 If the small programs are combinable, then they offer even a larger set
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meillo@5
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345 of functions than the single large program.
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meillo@45
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346 Hence, one gets two advantages out of writing small, combinable programs:
|
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meillo@45
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347 They are easier to write and they offer a greater set of functions through
|
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meillo@45
|
348 combination.
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meillo@5
|
349 .PP
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meillo@45
|
350 But there are also two main drawbacks of the toolchest approach.
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meillo@45
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351 First, one simple, standardized interface has to be sufficient.
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meillo@5
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352 If one feels the need for more ``logic'' than a stream of bytes,
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meillo@8
|
353 then a different approach might be of need.
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meillo@13
|
354 But it is also possible, that he just can not imagine a design where
|
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meillo@8
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355 a stream of bytes is sufficient.
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meillo@8
|
356 By becoming more familiar with the ``Unix style of thinking'',
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meillo@8
|
357 developers will more often and easier find simple designs where
|
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meillo@8
|
358 a stream of bytes is a sufficient interface.
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|
meillo@8
|
359 .PP
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|
meillo@8
|
360 The second drawback of a toolchest affects the users.
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|
meillo@45
|
361 A toolchest is often more difficult to use.
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meillo@9
|
362 It is necessary to become familiar with each of the tools,
|
|
meillo@5
|
363 to be able to use the right one in a given situation.
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|
meillo@45
|
364 Additionally, one needs to combine the tools in a senseful way himself.
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|
meillo@45
|
365 This is like a sharp knife \(en it is a powerful tool in the hand of a
|
|
meillo@45
|
366 master, but of no good value in the hand of an unskilled.
|
|
meillo@45
|
367 However, learning single, small tools of a toolchest is easier than
|
|
meillo@45
|
368 learning a complex tool.
|
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meillo@45
|
369 And the user will already have a basic understanding of a yet unknown tool,
|
|
meillo@45
|
370 if the tools of a toolchest have a common, consistent style.
|
|
meillo@45
|
371 He will be able to transfer knowledge over from one tool to another.
|
|
meillo@5
|
372 .PP
|
|
meillo@45
|
373 Moreover, the second drawback can be removed to a large extend
|
|
meillo@45
|
374 by adding wrappers around the basic tools.
|
|
meillo@45
|
375 Novice users do not need to learn several tools, if a professional wraps
|
|
meillo@45
|
376 complete command lines into a higher-level script.
|
|
meillo@5
|
377 Note that the wrapper script still calls the small tools;
|
|
meillo@45
|
378 it is just like a skin around them.
|
|
meillo@45
|
379 No complexity is added this way.
|
|
meillo@45
|
380 But new programs can get created out of existing one with very low effort.
|
|
meillo@5
|
381 .PP
|
|
meillo@5
|
382 A wrapper script for finding the five largest entries in the current directory
|
|
meillo@5
|
383 could look like this:
|
|
meillo@41
|
384 .DS
|
|
meillo@5
|
385 #!/bin/sh
|
|
meillo@5
|
386 du -s * | sort -nr | sed 5q
|
|
meillo@5
|
387 .DE
|
|
meillo@45
|
388 The script itself is just a text file that calls the command line,
|
|
meillo@45
|
389 which a professional user would type in directly.
|
|
meillo@45
|
390 It is probably worth to make the program flexible on the number of
|
|
meillo@45
|
391 entries it prints:
|
|
meillo@41
|
392 .DS
|
|
meillo@8
|
393 #!/bin/sh
|
|
meillo@8
|
394 num=5
|
|
meillo@8
|
395 [ $# -eq 1 ] && num="$1"
|
|
meillo@8
|
396 du -sh * | sort -nr | sed "${num}q"
|
|
meillo@8
|
397 .DE
|
|
meillo@8
|
398 This script acts like the one before, when called without an argument.
|
|
meillo@8
|
399 But one can also specify a numerical argument to define the number of lines to print.
|
|
meillo@45
|
400 One can surely imagine even more flexible versions, however,
|
|
meillo@45
|
401 they will still relay on the external programs,
|
|
meillo@45
|
402 which do the actual work.
|
|
meillo@5
|
403
|
|
meillo@48
|
404 .H 2 "A powerful shell
|
|
meillo@8
|
405 .LP
|
|
meillo@45
|
406 The Unix shell provides the possibility to combine small programs into large ones.
|
|
meillo@45
|
407 But a powerful shell is a great feature in other ways, too.
|
|
meillo@45
|
408 For instance by being scriptable.
|
|
meillo@45
|
409 Control statements are build into the shell.
|
|
meillo@45
|
410 The functions, however, are the normal programs of the system.
|
|
meillo@45
|
411 Thus, as the programs are already known,
|
|
meillo@45
|
412 learning to program in the shell becomes easy.
|
|
meillo@8
|
413 Using normal programs as functions in the shell programming language
|
|
meillo@10
|
414 is only possible because they are small and combinable tools in a toolchest style.
|
|
meillo@8
|
415 .PP
|
|
meillo@45
|
416 The Unix shell encourages to write small scripts,
|
|
meillo@45
|
417 by combining existing programs, because it is so easy to do.
|
|
meillo@8
|
418 This is a great step towards automation.
|
|
meillo@8
|
419 It is wonderful if the effort to automate a task equals the effort
|
|
meillo@45
|
420 to do the task a second time by hand.
|
|
meillo@45
|
421 If this holds,
|
|
meillo@45
|
422 then the user will be happy to automate everything he does more than once.
|
|
meillo@8
|
423 .PP
|
|
meillo@8
|
424 Small programs that do one job well, standardized interfaces between them,
|
|
meillo@8
|
425 a mechanism to combine parts to larger parts, and an easy way to automate tasks,
|
|
meillo@8
|
426 this will inevitably produce software leverage.
|
|
meillo@8
|
427 Getting multiple times the benefit of an investment is a great offer.
|
|
meillo@10
|
428 .PP
|
|
meillo@10
|
429 The shell also encourages rapid prototyping.
|
|
meillo@10
|
430 Many well known programs started as quickly hacked shell scripts,
|
|
meillo@10
|
431 and turned into ``real'' programs, written in C, later.
|
|
meillo@45
|
432 Building a prototype first, is a way to avoid the biggest problems
|
|
meillo@10
|
433 in application development.
|
|
meillo@45
|
434 Fred Brooks explains in ``No Silver Bullet'':
|
|
meillo@10
|
435 .[
|
|
meillo@44
|
436 brooks
|
|
meillo@44
|
437 no silver bullet
|
|
meillo@10
|
438 .]
|
|
meillo@10
|
439 .QP
|
|
meillo@10
|
440 The hardest single part of building a software system is deciding precisely what to build.
|
|
meillo@10
|
441 No other part of the conceptual work is so difficult as establishing the detailed
|
|
meillo@10
|
442 technical requirements, [...].
|
|
meillo@10
|
443 No other part of the work so cripples the resulting system if done wrong.
|
|
meillo@10
|
444 No other part is more difficult to rectify later.
|
|
meillo@10
|
445 .PP
|
|
meillo@45
|
446 Writing a prototype is a great method for becoming familiar with the requirements
|
|
meillo@45
|
447 and to run into real problems early.
|
|
meillo@47
|
448 .[ [
|
|
meillo@47
|
449 gancarz
|
|
meillo@47
|
450 unix philosophy
|
|
meillo@47
|
451 .], page 28 f.]
|
|
meillo@45
|
452 .PP
|
|
meillo@45
|
453 Prototyping is often seen as a first step in building a software.
|
|
meillo@10
|
454 This is, of course, good.
|
|
meillo@10
|
455 However, the Unix Philosophy has an \fIadditional\fP perspective on prototyping:
|
|
meillo@10
|
456 After having built the prototype, one might notice, that the prototype is already
|
|
meillo@10
|
457 \fIgood enough\fP.
|
|
meillo@45
|
458 Hence, no reimplementation, in a more sophisticated programming language,
|
|
meillo@45
|
459 might be of need, at least for the moment.
|
|
meillo@23
|
460 Maybe later, it might be necessary to rewrite the software, but not now.
|
|
meillo@45
|
461 By delaying further work, one keeps the flexibility to react on
|
|
meillo@10
|
462 changing requirements.
|
|
meillo@10
|
463 Software parts that are not written will not miss the requirements.
|
|
meillo@10
|
464
|
|
meillo@48
|
465 .H 2 "Worse is better
|
|
meillo@10
|
466 .LP
|
|
meillo@45
|
467 The Unix Philosophy aims for the 90% solution;
|
|
meillo@10
|
468 others call it the ``Worse is better'' approach.
|
|
meillo@47
|
469 Experience from real life projects shows:
|
|
meillo@10
|
470 .PP
|
|
meillo@45
|
471 (1) It is almost never possible to define the
|
|
meillo@10
|
472 requirements completely and correctly the first time.
|
|
meillo@45
|
473 Hence one should not try to; one will fail anyway.
|
|
meillo@45
|
474 .PP
|
|
meillo@45
|
475 (2) Requirements change during time.
|
|
meillo@10
|
476 Hence it is best to delay requirement-based design decisions as long as possible.
|
|
meillo@45
|
477 The software should be small and flexible as long as possible
|
|
meillo@10
|
478 to react on changing requirements.
|
|
meillo@10
|
479 Shell scripts, for example, are more easily adjusted as C programs.
|
|
meillo@45
|
480 .PP
|
|
meillo@45
|
481 (3) Maintenance work is hard work.
|
|
meillo@45
|
482 Hence, one should keep the amount of code as small as possible;
|
|
meillo@10
|
483 it should just fulfill the \fIcurrent\fP requirements.
|
|
meillo@45
|
484 Software parts that will be written in future,
|
|
meillo@45
|
485 do not need maintenance till then.
|
|
meillo@10
|
486 .PP
|
|
meillo@47
|
487 See Brooks' ``The Mythical Man-Month'' for reference.
|
|
meillo@47
|
488 .[ [
|
|
meillo@47
|
489 brooks
|
|
meillo@47
|
490 mythical man-month
|
|
meillo@47
|
491 .], page 115 ff.]
|
|
meillo@47
|
492 .PP
|
|
meillo@10
|
493 Starting with a prototype in a scripting language has several advantages:
|
|
meillo@10
|
494 .IP \(bu
|
|
meillo@10
|
495 As the initial effort is low, one will likely start right away.
|
|
meillo@10
|
496 .IP \(bu
|
|
meillo@10
|
497 As working parts are available soon, the real requirements can get identified soon.
|
|
meillo@10
|
498 .IP \(bu
|
|
meillo@45
|
499 When a software is usable and valuable, it gets used, and thus tested.
|
|
meillo@10
|
500 Hence problems will be found at early stages of the development.
|
|
meillo@10
|
501 .IP \(bu
|
|
meillo@10
|
502 The prototype might be enough for the moment,
|
|
meillo@45
|
503 thus further work on the software can get delayed to a time
|
|
meillo@10
|
504 when one knows better about the requirements and problems,
|
|
meillo@10
|
505 than now.
|
|
meillo@10
|
506 .IP \(bu
|
|
meillo@45
|
507 Implementing now only the parts that are actually needed at the moment,
|
|
meillo@45
|
508 introduces fewer programming and maintenance work.
|
|
meillo@10
|
509 .IP \(bu
|
|
meillo@10
|
510 If the global situation changes so that the software is not needed anymore,
|
|
meillo@10
|
511 then less effort was spent into the project, than it would have be
|
|
meillo@10
|
512 when a different approach had been used.
|
|
meillo@10
|
513
|
|
meillo@48
|
514 .H 2 "Upgrowth and survival of software
|
|
meillo@11
|
515 .LP
|
|
meillo@12
|
516 So far it was talked about \fIwriting\fP or \fIbuilding\fP software.
|
|
meillo@13
|
517 Although these are just verbs, they do imply a specific view on the work process
|
|
meillo@13
|
518 they describe.
|
|
meillo@12
|
519 The better verb, however, is to \fIgrow\fP.
|
|
meillo@12
|
520 Creating software in the sense of the Unix Philosophy is an incremental process.
|
|
meillo@12
|
521 It starts with a first prototype, which evolves as requirements change.
|
|
meillo@12
|
522 A quickly hacked shell script might become a large, sophisticated,
|
|
meillo@13
|
523 compiled program this way.
|
|
meillo@13
|
524 Its lifetime begins with the initial prototype and ends when the software is not used anymore.
|
|
meillo@45
|
525 While being alive it will get extended, rearranged, rebuilt.
|
|
meillo@12
|
526 Growing software matches the view that ``software is never finished. It is only released.''
|
|
meillo@46
|
527 .[ [
|
|
meillo@44
|
528 gancarz
|
|
meillo@44
|
529 unix philosophy
|
|
meillo@46
|
530 .], page 26]
|
|
meillo@12
|
531 .PP
|
|
meillo@13
|
532 Software can be seen as being controlled by evolutionary processes.
|
|
meillo@13
|
533 Successful software is software that is used by many for a long time.
|
|
meillo@12
|
534 This implies that the software is needed, useful, and better than alternatives.
|
|
meillo@12
|
535 Darwin talks about: ``The survival of the fittest.''
|
|
meillo@12
|
536 .[
|
|
meillo@44
|
537 darwin
|
|
meillo@44
|
538 origin of species
|
|
meillo@12
|
539 .]
|
|
meillo@12
|
540 Transferred to software: The most successful software, is the fittest,
|
|
meillo@12
|
541 is the one that survives.
|
|
meillo@13
|
542 (This may be at the level of one creature, or at the level of one species.)
|
|
meillo@13
|
543 The fitness of software is affected mainly by four properties:
|
|
meillo@15
|
544 portability of code, portability of data, range of usability, and reusability of parts.
|
|
meillo@13
|
545 .PP
|
|
meillo@15
|
546 (1)
|
|
meillo@15
|
547 .I "Portability of code
|
|
meillo@15
|
548 means, using high-level programming languages,
|
|
meillo@13
|
549 sticking to the standard,
|
|
meillo@47
|
550 .[ [
|
|
meillo@47
|
551 kernighan pike
|
|
meillo@47
|
552 practice of programming
|
|
meillo@47
|
553 .], chapter\|8]
|
|
meillo@13
|
554 and avoiding optimizations that introduce dependencies on specific hardware.
|
|
meillo@13
|
555 Hardware has a much lower lifetime than software.
|
|
meillo@13
|
556 By chaining software to a specific hardware,
|
|
meillo@13
|
557 the software's lifetime gets shortened to that of this hardware.
|
|
meillo@13
|
558 In contrast, software should be easy to port \(en
|
|
meillo@23
|
559 adaptation is the key to success.
|
|
meillo@13
|
560 .PP
|
|
meillo@15
|
561 (2)
|
|
meillo@15
|
562 .I "Portability of data
|
|
meillo@15
|
563 is best achieved by avoiding binary representations
|
|
meillo@13
|
564 to store data, because binary representations differ from machine to machine.
|
|
meillo@23
|
565 Textual representation is favored.
|
|
meillo@45
|
566 Historically, \s-1ASCII\s0 was the charset of choice.
|
|
meillo@45
|
567 For the future, \s-1UTF\s0-8 might be the better choice.
|
|
meillo@13
|
568 Important is that it is a plain text representation in a
|
|
meillo@13
|
569 very common charset encoding.
|
|
meillo@13
|
570 Apart from being able to transfer data between machines,
|
|
meillo@45
|
571 readable data has the great advantage, that humans are able to directly
|
|
meillo@45
|
572 read and edit it with text editors and other tools from the Unix toolchest.
|
|
meillo@47
|
573 .[ [
|
|
meillo@47
|
574 gancarz
|
|
meillo@47
|
575 unix philosophy
|
|
meillo@47
|
576 .], page 56 ff.]
|
|
meillo@13
|
577 .PP
|
|
meillo@15
|
578 (3)
|
|
meillo@15
|
579 A large
|
|
meillo@15
|
580 .I "range of usability
|
|
meillo@23
|
581 ensures good adaptation, and thus good survival.
|
|
meillo@13
|
582 It is a special distinction if a software becomes used in fields of action,
|
|
meillo@13
|
583 the original authors did never imagine.
|
|
meillo@13
|
584 Software that solves problems in a general way will likely be used
|
|
meillo@45
|
585 for many kinds of similar problems.
|
|
meillo@45
|
586 Being too specific limits the range of usability.
|
|
meillo@13
|
587 Requirements change through time, thus use cases change or even vanish.
|
|
meillo@45
|
588 As a good example in this point,
|
|
meillo@13
|
589 Allman identifies flexibility to be one major reason for sendmail's success:
|
|
meillo@13
|
590 .[
|
|
meillo@44
|
591 allman
|
|
meillo@44
|
592 sendmail
|
|
meillo@13
|
593 .]
|
|
meillo@13
|
594 .QP
|
|
meillo@13
|
595 Second, I limited myself to the routing function [...].
|
|
meillo@13
|
596 This was a departure from the dominant thought of the time, [...].
|
|
meillo@13
|
597 .QP
|
|
meillo@45
|
598 Third, the sendmail configuration file was flexible enough to adapt
|
|
meillo@13
|
599 to a rapidly changing world [...].
|
|
meillo@12
|
600 .LP
|
|
meillo@45
|
601 Successful software adapts itself to the changing world.
|
|
meillo@13
|
602 .PP
|
|
meillo@15
|
603 (4)
|
|
meillo@15
|
604 .I "Reuse of parts
|
|
meillo@15
|
605 is even one step further.
|
|
meillo@13
|
606 A software may completely lose its field of action,
|
|
meillo@13
|
607 but parts of which the software is build may be general and independent enough
|
|
meillo@13
|
608 to survive this death.
|
|
meillo@13
|
609 If software is build by combining small independent programs,
|
|
meillo@45
|
610 then these parts are readily available for reuse.
|
|
meillo@13
|
611 Who cares if the large program is a failure,
|
|
meillo@13
|
612 but parts of it become successful instead?
|
|
meillo@10
|
613
|
|
meillo@48
|
614 .H 2 "Summary
|
|
meillo@0
|
615 .LP
|
|
meillo@45
|
616 This chapter explained central ideas of the Unix Philosophy.
|
|
meillo@45
|
617 For each of the ideas, the advantages they introduce were explained.
|
|
meillo@45
|
618 The Unix Philosophy are guidelines that help to write more valuable software.
|
|
meillo@14
|
619 From the view point of a software developer or software designer,
|
|
meillo@14
|
620 the Unix Philosophy provides answers to many software design problem.
|
|
meillo@14
|
621 .PP
|
|
meillo@14
|
622 The various ideas of the Unix Philosophy are very interweaved
|
|
meillo@14
|
623 and can hardly be applied independently.
|
|
meillo@14
|
624 However, the probably most important messages are:
|
|
meillo@45
|
625 .I "``Keep it simple!''" ,
|
|
meillo@14
|
626 .I "``Do one thing well!''" ,
|
|
meillo@14
|
627 and
|
|
meillo@14
|
628 .I "``Use software leverage!''
|
|
meillo@0
|
629
|
|
meillo@8
|
630
|
|
meillo@8
|
631
|
|
meillo@48
|
632 .H 1 "Case study: \s-1MH\s0
|
|
meillo@18
|
633 .LP
|
|
meillo@30
|
634 The previous chapter introduced and explained the Unix Philosophy
|
|
meillo@18
|
635 from a general point of view.
|
|
meillo@30
|
636 The driving force were the guidelines; references to
|
|
meillo@18
|
637 existing software were given only sparsely.
|
|
meillo@18
|
638 In this and the next chapter, concrete software will be
|
|
meillo@18
|
639 the driving force in the discussion.
|
|
meillo@18
|
640 .PP
|
|
meillo@23
|
641 This first case study is about the mail user agents (\s-1MUA\s0)
|
|
meillo@23
|
642 \s-1MH\s0 (``mail handler'') and its descendent \fInmh\fP
|
|
meillo@23
|
643 (``new mail handler'').
|
|
meillo@47
|
644 .[
|
|
meillo@47
|
645 nmh website
|
|
meillo@47
|
646 .]
|
|
meillo@23
|
647 \s-1MUA\s0s provide functions to read, compose, and organize mail,
|
|
meillo@45
|
648 but (ideally) not to transfer it.
|
|
meillo@45
|
649 In this document, the name \s-1MH\s0 will be used to include nmh.
|
|
meillo@19
|
650 A distinction will only be made if differences between
|
|
meillo@45
|
651 \s-1MH\s0 and nmh are described.
|
|
meillo@18
|
652
|
|
meillo@0
|
653
|
|
meillo@48
|
654 .H 2 "Historical background
|
|
meillo@0
|
655 .LP
|
|
meillo@19
|
656 Electronic mail was available in Unix very early.
|
|
meillo@30
|
657 The first \s-1MUA\s0 on Unix was \f(CWmail\fP,
|
|
meillo@30
|
658 which was already present in the First Edition.
|
|
meillo@46
|
659 .[ [
|
|
meillo@44
|
660 salus
|
|
meillo@44
|
661 quarter century of unix
|
|
meillo@46
|
662 .], page 41 f.]
|
|
meillo@45
|
663 It was a small program that either printed the user's mailbox file
|
|
meillo@45
|
664 or appended text to someone elses mailbox file,
|
|
meillo@19
|
665 depending on the command line arguments.
|
|
meillo@19
|
666 .[
|
|
meillo@44
|
667 manual mail(1)
|
|
meillo@19
|
668 .]
|
|
meillo@19
|
669 It was a program that did one job well.
|
|
meillo@23
|
670 This job was emailing, which was very simple then.
|
|
meillo@19
|
671 .PP
|
|
meillo@23
|
672 Later, emailing became more powerful, and thus more complex.
|
|
meillo@19
|
673 The simple \f(CWmail\fP, which knew nothing of subjects,
|
|
meillo@19
|
674 independent handling of single messages,
|
|
meillo@45
|
675 and long-time email storage, was not powerful enough anymore.
|
|
meillo@45
|
676 In 1978 at Berkeley, Kurt Shoens wrote \fIMail\fP (with capital `M')
|
|
meillo@45
|
677 to provide additional functions for emailing.
|
|
meillo@19
|
678 Mail was still one program, but now it was large and did
|
|
meillo@19
|
679 several jobs.
|
|
meillo@23
|
680 Its user interface is modeled after the one of \fIed\fP.
|
|
meillo@19
|
681 It is designed for humans, but is still scriptable.
|
|
meillo@23
|
682 \fImailx\fP is the adaptation of Berkeley Mail into System V.
|
|
meillo@19
|
683 .[
|
|
meillo@44
|
684 ritter
|
|
meillo@44
|
685 mailx history
|
|
meillo@19
|
686 .]
|
|
meillo@30
|
687 Elm, pine, mutt, and a whole bunch of graphical \s-1MUA\s0s
|
|
meillo@19
|
688 followed Mail's direction.
|
|
meillo@19
|
689 They are large, monolithic programs which include all emailing functions.
|
|
meillo@19
|
690 .PP
|
|
meillo@23
|
691 A different way was taken by the people of \s-1RAND\s0 Corporation.
|
|
meillo@38
|
692 In the beginning, they also had used a monolithic mail system,
|
|
meillo@30
|
693 called \s-1MS\s0 (for ``mail system'').
|
|
meillo@19
|
694 But in 1977, Stockton Gaines and Norman Shapiro
|
|
meillo@19
|
695 came up with a proposal of a new email system concept \(en
|
|
meillo@45
|
696 one that honored the Unix Philosophy.
|
|
meillo@19
|
697 The concept was implemented by Bruce Borden in 1978 and 1979.
|
|
meillo@19
|
698 This was the birth of \s-1MH\s0 \(en the ``mail handler''.
|
|
meillo@18
|
699 .PP
|
|
meillo@18
|
700 Since then, \s-1RAND\s0, the University of California at Irvine and
|
|
meillo@19
|
701 at Berkeley, and several others have contributed to the software.
|
|
meillo@18
|
702 However, it's core concepts remained the same.
|
|
meillo@23
|
703 In the late 90s, when development of \s-1MH\s0 slowed down,
|
|
meillo@19
|
704 Richard Coleman started with \fInmh\fP, the new mail handler.
|
|
meillo@45
|
705 His goal was to improve \s-1MH\s0 especially in regard of
|
|
meillo@23
|
706 the requirements of modern emailing.
|
|
meillo@19
|
707 Today, nmh is developed by various people on the Internet.
|
|
meillo@18
|
708 .[
|
|
meillo@44
|
709 ware
|
|
meillo@44
|
710 rand history
|
|
meillo@18
|
711 .]
|
|
meillo@18
|
712 .[
|
|
meillo@44
|
713 peek
|
|
meillo@44
|
714 mh
|
|
meillo@18
|
715 .]
|
|
meillo@0
|
716
|
|
meillo@48
|
717 .H 2 "Contrasts to monolithic mail systems
|
|
meillo@0
|
718 .LP
|
|
meillo@19
|
719 All \s-1MUA\s0s are monolithic, except \s-1MH\s0.
|
|
meillo@38
|
720 Although there might actually exist further, very little known,
|
|
meillo@30
|
721 toolchest \s-1MUA\s0s, this statement reflects the situation pretty well.
|
|
meillo@19
|
722 .PP
|
|
meillo@30
|
723 Monolithic \s-1MUA\s0s gather all their functions in one program.
|
|
meillo@30
|
724 In contrast, \s-1MH\s0 is a toolchest of many small tools \(en one for each job.
|
|
meillo@23
|
725 Following is a list of important programs of \s-1MH\s0's toolchest
|
|
meillo@30
|
726 and their function.
|
|
meillo@30
|
727 It gives a feeling of how the toolchest looks like.
|
|
meillo@19
|
728 .IP \(bu
|
|
meillo@19
|
729 .CW inc :
|
|
meillo@30
|
730 incorporate new mail (this is how mail enters the system)
|
|
meillo@19
|
731 .IP \(bu
|
|
meillo@19
|
732 .CW scan :
|
|
meillo@19
|
733 list messages in folder
|
|
meillo@19
|
734 .IP \(bu
|
|
meillo@19
|
735 .CW show :
|
|
meillo@19
|
736 show message
|
|
meillo@19
|
737 .IP \(bu
|
|
meillo@19
|
738 .CW next\fR/\fPprev :
|
|
meillo@19
|
739 show next/previous message
|
|
meillo@19
|
740 .IP \(bu
|
|
meillo@19
|
741 .CW folder :
|
|
meillo@19
|
742 change current folder
|
|
meillo@19
|
743 .IP \(bu
|
|
meillo@19
|
744 .CW refile :
|
|
meillo@45
|
745 refile message into different folder
|
|
meillo@19
|
746 .IP \(bu
|
|
meillo@19
|
747 .CW rmm :
|
|
meillo@19
|
748 remove message
|
|
meillo@19
|
749 .IP \(bu
|
|
meillo@19
|
750 .CW comp :
|
|
meillo@45
|
751 compose new message
|
|
meillo@19
|
752 .IP \(bu
|
|
meillo@19
|
753 .CW repl :
|
|
meillo@45
|
754 reply to message
|
|
meillo@19
|
755 .IP \(bu
|
|
meillo@19
|
756 .CW forw :
|
|
meillo@45
|
757 forward message
|
|
meillo@19
|
758 .IP \(bu
|
|
meillo@19
|
759 .CW send :
|
|
meillo@45
|
760 send prepared message (this is how mail leaves the system)
|
|
meillo@0
|
761 .LP
|
|
meillo@19
|
762 \s-1MH\s0 has no special user interface like monolithic \s-1MUA\s0s have.
|
|
meillo@19
|
763 The user does not leave the shell to run \s-1MH\s0,
|
|
meillo@45
|
764 instead he uses the various \s-1MH\s0 programs within the shell.
|
|
meillo@23
|
765 Using a monolithic program with a captive user interface
|
|
meillo@23
|
766 means ``entering'' the program, using it, and ``exiting'' the program.
|
|
meillo@23
|
767 Using toolchests like \s-1MH\s0 means running programs,
|
|
meillo@45
|
768 alone or in combination with others, also from other toolchests,
|
|
meillo@23
|
769 without leaving the shell.
|
|
meillo@30
|
770
|
|
meillo@48
|
771 .H 2 "Data storage
|
|
meillo@30
|
772 .LP
|
|
meillo@34
|
773 \s-1MH\s0's mail storage is a directory tree under the user's
|
|
meillo@34
|
774 \s-1MH\s0 directory (usually \f(CW$HOME/Mail\fP),
|
|
meillo@34
|
775 where mail folders are directories and mail messages are text files
|
|
meillo@34
|
776 within them.
|
|
meillo@34
|
777 Each mail folder contains a file \f(CW.mh_sequences\fP which lists
|
|
meillo@45
|
778 the public message sequences of that folder,
|
|
meillo@45
|
779 for instance the \fIunseen\fP sequence for new messages.
|
|
meillo@34
|
780 Mail messages are text files located in a mail folder.
|
|
meillo@34
|
781 The files contain the messages as they were received.
|
|
meillo@45
|
782 They are named by ascending numbers in each folder.
|
|
meillo@19
|
783 .PP
|
|
meillo@30
|
784 This mailbox format is called ``\s-1MH\s0'' after the \s-1MUA\s0.
|
|
meillo@30
|
785 Alternatives are \fImbox\fP and \fImaildir\fP.
|
|
meillo@30
|
786 In the mbox format all messages are stored within one file.
|
|
meillo@30
|
787 This was a good solution in the early days, when messages
|
|
meillo@30
|
788 were only a few lines of text and were deleted soon.
|
|
meillo@30
|
789 Today, when single messages often include several megabytes
|
|
meillo@30
|
790 of attachments, it is a bad solution.
|
|
meillo@30
|
791 Another disadvantage of the mbox format is that it is
|
|
meillo@30
|
792 more difficult to write tools that work on mail messages,
|
|
meillo@30
|
793 because it is always necessary to first find and extract
|
|
meillo@30
|
794 the relevant message in the mbox file.
|
|
meillo@45
|
795 With the \s-1MH\s0 mailbox format, each message is a separate file.
|
|
meillo@30
|
796 Also, the problem of concurrent access to one mailbox is
|
|
meillo@30
|
797 reduced to the problem of concurrent access to one message.
|
|
meillo@45
|
798 The maildir format is generally similar to the \s-1MH\s0 format,
|
|
meillo@30
|
799 but modified towards guaranteed reliability.
|
|
meillo@30
|
800 This involves some complexity, unfortunately.
|
|
meillo@34
|
801 .PP
|
|
meillo@34
|
802 Working with \s-1MH\s0's toolchest on mailboxes is much like
|
|
meillo@34
|
803 working with Unix' toolchest on directory trees:
|
|
meillo@34
|
804 \f(CWscan\fP is like \f(CWls\fP,
|
|
meillo@34
|
805 \f(CWshow\fP is like \f(CWcat\fP,
|
|
meillo@34
|
806 \f(CWfolder\fP is like \f(CWcd\fP and \f(CWpwd\fP,
|
|
meillo@34
|
807 \f(CWrefile\fP is like \f(CWmv\fP,
|
|
meillo@34
|
808 and \f(CWrmm\fP is like \f(CWrm\fP.
|
|
meillo@34
|
809 .PP
|
|
meillo@45
|
810 \s-1MH\s0 extends the context of processes in Unix by two more items,
|
|
meillo@45
|
811 for its tools:
|
|
meillo@34
|
812 .IP \(bu
|
|
meillo@34
|
813 The current mail folder, which is similar to the current working directory.
|
|
meillo@34
|
814 For mail folders, \f(CWfolder\fP provides the corresponding functionality
|
|
meillo@34
|
815 of \f(CWcd\fP and \f(CWpwd\fP for directories.
|
|
meillo@34
|
816 .IP \(bu
|
|
meillo@34
|
817 Sequences, which are named sets of messages in a mail folder.
|
|
meillo@34
|
818 The current message, relative to a mail folder, is a special sequence.
|
|
meillo@34
|
819 It enables commands like \f(CWnext\fP and \f(CWprev\fP.
|
|
meillo@34
|
820 .LP
|
|
meillo@45
|
821 In contrast to Unix' context, which is maintained by the kernel,
|
|
meillo@45
|
822 \s-1MH\s0's context must be maintained by the tools themselves.
|
|
meillo@45
|
823 Usually there is one context per user, which resides in his
|
|
meillo@45
|
824 \f(CWcontext\fP file in the \s-1MH\s0 directory,
|
|
meillo@45
|
825 but a user can have several contexts, too.
|
|
meillo@45
|
826 Public sequences are an exception, as they belong to a mail folder,
|
|
meillo@45
|
827 and reside in the \f(CW.mh_sequences\fP file there.
|
|
meillo@34
|
828 .[
|
|
meillo@44
|
829 man page mh-profile mh-sequence
|
|
meillo@34
|
830 .]
|
|
meillo@20
|
831
|
|
meillo@48
|
832 .H 2 "Discussion of the design
|
|
meillo@0
|
833 .LP
|
|
meillo@45
|
834 This section discusses \s-1MH\s0 in regard to the tenets
|
|
meillo@45
|
835 of the Unix Philosophy that Gancarz identified.
|
|
meillo@20
|
836
|
|
meillo@20
|
837 .PP
|
|
meillo@33
|
838 .B "Small is beautiful
|
|
meillo@20
|
839 and
|
|
meillo@33
|
840 .B "do one thing well
|
|
meillo@20
|
841 are two design goals that are directly visible in \s-1MH\s0.
|
|
meillo@45
|
842 Gancarz actually presents \s-1MH\s0 in his book as example under the
|
|
meillo@45
|
843 headline ``Making \s-1UNIX\s0 Do One Thing Well'':
|
|
meillo@46
|
844 .[ [
|
|
meillo@44
|
845 gancarz
|
|
meillo@44
|
846 unix philosophy
|
|
meillo@46
|
847 .], page 125 ff.]
|
|
meillo@20
|
848 .QP
|
|
meillo@20
|
849 [\s-1MH\s0] consists of a series of programs which
|
|
meillo@20
|
850 when combined give the user an enormous ability
|
|
meillo@20
|
851 to manipulate electronic mail messages.
|
|
meillo@20
|
852 A complex application, it shows that not only is it
|
|
meillo@20
|
853 possible to build large applications from smaller
|
|
meillo@20
|
854 components, but also that such designs are actually preferable.
|
|
meillo@20
|
855 .LP
|
|
meillo@45
|
856 The various programs of \s-1MH\s0 were relatively easy to write,
|
|
meillo@45
|
857 because each of them is small, limited to one function,
|
|
meillo@23
|
858 and has clear boundaries.
|
|
meillo@20
|
859 For the same reasons, they are also good to maintain.
|
|
meillo@20
|
860 Further more, the system can easily get extended.
|
|
meillo@20
|
861 One only needs to put a new program into the toolchest.
|
|
meillo@23
|
862 This was done, for instance, when \s-1MIME\s0 support was added
|
|
meillo@20
|
863 (e.g. \f(CWmhbuild\fP).
|
|
meillo@20
|
864 Also, different programs can exist to do the basically same job
|
|
meillo@20
|
865 in different ways (e.g. in nmh: \f(CWshow\fP and \f(CWmhshow\fP).
|
|
meillo@45
|
866 .PP
|
|
meillo@20
|
867 If someone needs a mail system with some additionally
|
|
meillo@45
|
868 functions that are not available anywhere yet, he best expands a
|
|
meillo@45
|
869 toolchest system like \s-1MH\s0.
|
|
meillo@45
|
870 There he can add new functionality by simply adding additional
|
|
meillo@45
|
871 programs to the toolchest.
|
|
meillo@45
|
872 There he does not risk to break existing functionality by doing so.
|
|
meillo@20
|
873
|
|
meillo@20
|
874 .PP
|
|
meillo@34
|
875 .B "Store data in flat text files
|
|
meillo@34
|
876 is followed by \s-1MH\s0.
|
|
meillo@34
|
877 This is not surprising, because email messages are already plain text.
|
|
meillo@34
|
878 \s-1MH\s0 stores the messages as it receives them,
|
|
meillo@45
|
879 thus any other tool that works on \s-1RFC\s0\|2822 mail messages can operate
|
|
meillo@34
|
880 on the messages in an \s-1MH\s0 mailbox.
|
|
meillo@45
|
881 All other files \s-1MH\s0 uses are plain text, too.
|
|
meillo@34
|
882 It is therefore possible and encouraged to use the text processing
|
|
meillo@34
|
883 tools of Unix' toolchest to extend \s-1MH\s0's toolchest.
|
|
meillo@20
|
884
|
|
meillo@20
|
885 .PP
|
|
meillo@33
|
886 .B "Avoid captive user interfaces" .
|
|
meillo@19
|
887 \s-1MH\s0 is perfectly suited for non-interactive use.
|
|
meillo@19
|
888 It offers all functions directly and without captive user interfaces.
|
|
meillo@30
|
889 If, nonetheless, users want a graphical user interface,
|
|
meillo@45
|
890 they can have it with \fIxmh\fP or \fIexmh\fP.
|
|
meillo@19
|
891 These are graphical frontends for the \s-1MH\s0 toolchest.
|
|
meillo@19
|
892 This means, all email-related work is still done by \s-1MH\s0 tools,
|
|
meillo@45
|
893 but the frontend calls the appropriate commands when the user
|
|
meillo@30
|
894 clicks on buttons.
|
|
meillo@45
|
895 .PP
|
|
meillo@20
|
896 Providing easy-to-use user interfaces in form of frontends is a good
|
|
meillo@19
|
897 approach, because it does not limit the power of the backend itself.
|
|
meillo@20
|
898 The frontend will anyway only be able to make a subset of the
|
|
meillo@23
|
899 backend's power and flexibility available to the user.
|
|
meillo@20
|
900 But if it is a separate program,
|
|
meillo@20
|
901 then the missing parts can still be accessed at the backend directly.
|
|
meillo@19
|
902 If it is integrated, then this will hardly be possible.
|
|
meillo@45
|
903 An additional advantage is the possibility to have different frontends
|
|
meillo@45
|
904 to the same backend.
|
|
meillo@19
|
905
|
|
meillo@19
|
906 .PP
|
|
meillo@33
|
907 .B "Choose portability over efficiency
|
|
meillo@20
|
908 and
|
|
meillo@33
|
909 .B "use shell scripts to increase leverage and portability" .
|
|
meillo@20
|
910 These two tenets are indirectly, but nicely, demonstrated by
|
|
meillo@30
|
911 Bolsky and Korn in their book about the Korn Shell.
|
|
meillo@20
|
912 .[
|
|
meillo@44
|
913 bolsky korn
|
|
meillo@44
|
914 korn shell
|
|
meillo@20
|
915 .]
|
|
meillo@45
|
916 Chapter\|18 of the book shows a basic implementation
|
|
meillo@20
|
917 of a subset of \s-1MH\s0 in ksh scripts.
|
|
meillo@45
|
918 Of course, this is just a demonstration, but a brilliant one.
|
|
meillo@20
|
919 It shows how quickly one can implement such a prototype with shell scripts,
|
|
meillo@20
|
920 and how readable they are.
|
|
meillo@20
|
921 The implementation in the scripting language may not be very fast,
|
|
meillo@20
|
922 but it can be fast enough though, and this is all that matters.
|
|
meillo@20
|
923 By having the code in an interpreted language, like the shell,
|
|
meillo@20
|
924 portability becomes a minor issue, if we assume the interpreter
|
|
meillo@20
|
925 to be widespread.
|
|
meillo@45
|
926 .PP
|
|
meillo@20
|
927 This demonstration also shows how easy it is to create single programs
|
|
meillo@20
|
928 of a toolchest software.
|
|
meillo@45
|
929 Eight tools (two of them have multiple names) and 16 functions
|
|
meillo@45
|
930 with supporting code are presented to the reader.
|
|
meillo@45
|
931 The tools comprise less than 40 lines of ksh each,
|
|
meillo@30
|
932 in total about 200 lines.
|
|
meillo@45
|
933 The functions comprise less than 80 lines of ksh each,
|
|
meillo@30
|
934 in total about 450 lines.
|
|
meillo@20
|
935 Such small software is easy to write, easy to understand,
|
|
meillo@20
|
936 and thus easy to maintain.
|
|
meillo@23
|
937 A toolchest improves the possibility to only write some parts
|
|
meillo@20
|
938 and though create a working result.
|
|
meillo@45
|
939 Expanding the toolchest, even without global changes,
|
|
meillo@45
|
940 will likely be possible.
|
|
meillo@20
|
941
|
|
meillo@20
|
942 .PP
|
|
meillo@33
|
943 .B "Use software leverage to your advantage
|
|
meillo@20
|
944 and the lesser tenet
|
|
meillo@33
|
945 .B "allow the user to tailor the environment
|
|
meillo@20
|
946 are ideally followed in the design of \s-1MH\s0.
|
|
meillo@21
|
947 Tailoring the environment is heavily encouraged by the ability to
|
|
meillo@30
|
948 directly define default options to programs.
|
|
meillo@30
|
949 It is even possible to define different default options
|
|
meillo@45
|
950 depending on the name under which a program is called.
|
|
meillo@45
|
951 Software leverage is heavily encouraged by the ease of
|
|
meillo@45
|
952 creating shell scripts that run a specific command line,
|
|
meillo@30
|
953 built of several \s-1MH\s0 programs.
|
|
meillo@21
|
954 There is few software that so much wants users to tailor their
|
|
meillo@21
|
955 environment and to leverage the use of the software, like \s-1MH\s0.
|
|
meillo@45
|
956 .PP
|
|
meillo@21
|
957 Just to make one example:
|
|
meillo@23
|
958 One might prefer a different listing format for the \f(CWscan\fP
|
|
meillo@21
|
959 program.
|
|
meillo@30
|
960 It is possible to take one of the distributed format files
|
|
meillo@21
|
961 or to write one yourself.
|
|
meillo@21
|
962 To use the format as default for \f(CWscan\fP, a single line,
|
|
meillo@21
|
963 reading
|
|
meillo@21
|
964 .DS
|
|
meillo@21
|
965 scan: -form FORMATFILE
|
|
meillo@21
|
966 .DE
|
|
meillo@21
|
967 must be added to \f(CW.mh_profile\fP.
|
|
meillo@21
|
968 If one wants this different format as an additional command,
|
|
meillo@23
|
969 instead of changing the default, he needs to create a link to
|
|
meillo@23
|
970 \f(CWscan\fP, for instance titled \f(CWscan2\fP.
|
|
meillo@21
|
971 The line in \f(CW.mh_profile\fP would then start with \f(CWscan2\fP,
|
|
meillo@45
|
972 as the option should only be in effect for a program that is called as
|
|
meillo@21
|
973 \f(CWscan2\fP.
|
|
meillo@20
|
974
|
|
meillo@20
|
975 .PP
|
|
meillo@33
|
976 .B "Make every program a filter
|
|
meillo@21
|
977 is hard to find in \s-1MH\s0.
|
|
meillo@21
|
978 The reason therefore is that most of \s-1MH\s0's tools provide
|
|
meillo@45
|
979 basic file system operations for mailboxes.
|
|
meillo@45
|
980 It is the same reason because of which \f(CWls\fP, \f(CWcp\fP, \f(CWmv\fP,
|
|
meillo@45
|
981 and \f(CWrm\fP aren't filters neither.
|
|
meillo@23
|
982 \s-1MH\s0 does not provide many filters itself, but it is a basis
|
|
meillo@23
|
983 to write filters for.
|
|
meillo@45
|
984 An example would be a mail text highlighter,
|
|
meillo@30
|
985 that means a program that makes use of a color terminal to display
|
|
meillo@30
|
986 header lines, quotations, and signatures in distinct colors.
|
|
meillo@45
|
987 The author's version of such a program is an awk script with 25 lines.
|
|
meillo@21
|
988
|
|
meillo@21
|
989 .PP
|
|
meillo@33
|
990 .B "Build a prototype as soon as possible
|
|
meillo@21
|
991 was again well followed by \s-1MH\s0.
|
|
meillo@21
|
992 This tenet, of course, focuses on early development, which is
|
|
meillo@21
|
993 long time ago for \s-1MH\s0.
|
|
meillo@21
|
994 But without following this guideline at the very beginning,
|
|
meillo@23
|
995 Bruce Borden may have not convinced the management of \s-1RAND\s0
|
|
meillo@23
|
996 to ever create \s-1MH\s0.
|
|
meillo@23
|
997 In Bruce' own words:
|
|
meillo@46
|
998 .[ [
|
|
meillo@44
|
999 ware rand history
|
|
meillo@46
|
1000 .], page 132]
|
|
meillo@21
|
1001 .QP
|
|
meillo@45
|
1002 [...] but [Stockton Gaines and Norm Shapiro] were not able
|
|
meillo@23
|
1003 to convince anyone that such a system would be fast enough to be usable.
|
|
meillo@21
|
1004 I proposed a very short project to prove the basic concepts,
|
|
meillo@21
|
1005 and my management agreed.
|
|
meillo@21
|
1006 Looking back, I realize that I had been very lucky with my first design.
|
|
meillo@21
|
1007 Without nearly enough design work,
|
|
meillo@21
|
1008 I built a working environment and some header files
|
|
meillo@21
|
1009 with key structures and wrote the first few \s-1MH\s0 commands:
|
|
meillo@21
|
1010 inc, show/next/prev, and comp.
|
|
meillo@21
|
1011 [...]
|
|
meillo@21
|
1012 With these three, I was able to convince people that the structure was viable.
|
|
meillo@21
|
1013 This took about three weeks.
|
|
meillo@0
|
1014
|
|
meillo@48
|
1015 .H 2 "Problems
|
|
meillo@0
|
1016 .LP
|
|
meillo@45
|
1017 \s-1MH\s0 is not without problems.
|
|
meillo@30
|
1018 There are two main problems: one is technical, the other is about human behavior.
|
|
meillo@22
|
1019 .PP
|
|
meillo@22
|
1020 \s-1MH\s0 is old and email today is very different to email in the time
|
|
meillo@22
|
1021 when \s-1MH\s0 was designed.
|
|
meillo@45
|
1022 \s-1MH\s0 adapted to the changes pretty well, but it is limited, though.
|
|
meillo@22
|
1023 \s-1MIME\s0 support and support for different character encodings
|
|
meillo@22
|
1024 is available, but only on a moderate level.
|
|
meillo@45
|
1025 This comes from limited development resources.
|
|
meillo@45
|
1026 More active developers could quickly change this.
|
|
meillo@45
|
1027 But \s-1MH\s0 is also limited by design, which is the larger problem.
|
|
meillo@22
|
1028 \s-1IMAP\s0, for example, conflicts with \s-1MH\s0's design to a large extend.
|
|
meillo@22
|
1029 These design conflicts are not easily solvable.
|
|
meillo@22
|
1030 Possibly, they require a redesign.
|
|
meillo@45
|
1031 \s-1IMAP\s0 may be too different to the classic mail model,
|
|
meillo@45
|
1032 which \s-1MH\s0 covers, so that \s-1MH\s0 may never support it well.
|
|
meillo@22
|
1033 .PP
|
|
meillo@45
|
1034 The other kind of problem are human habits.
|
|
meillo@45
|
1035 In this world, where almost all \s-1MUA\s0s are monolithic,
|
|
meillo@22
|
1036 it is very difficult to convince people to use a toolbox style \s-1MUA\s0
|
|
meillo@22
|
1037 like \s-1MH\s0.
|
|
meillo@45
|
1038 The habits are so strong, that even people who understand the concept
|
|
meillo@30
|
1039 and advantages of \s-1MH\s0 do not like to switch,
|
|
meillo@30
|
1040 simply because \s-1MH\s0 is different.
|
|
meillo@30
|
1041 Unfortunately, the frontends to \s-1MH\s0, which could provide familiar look'n'feel,
|
|
meillo@45
|
1042 are quite outdated and thus not very appealing, compared to the modern interfaces
|
|
meillo@45
|
1043 of many monolithic \s-1MUA\s0s.
|
|
meillo@20
|
1044
|
|
meillo@48
|
1045 NH 2 "Summary \s-1MH\s0
|
|
meillo@20
|
1046 .LP
|
|
meillo@45
|
1047 \s-1MH\s0 is an \s-1MUA\s0 that follows the Unix Philosophy in its design.
|
|
meillo@31
|
1048 It consists of a toolchest of small tools, each of them does one job well.
|
|
meillo@31
|
1049 The toolchest approach offers great flexibility to the user.
|
|
meillo@45
|
1050 It is possible to utilize the complete power of the Unix shell with \s-1MH\s0.
|
|
meillo@31
|
1051 This makes \s-1MH\s0 a very powerful mail system.
|
|
meillo@45
|
1052 Extending and customizing \s-1MH\s0 is easy and encouraged.
|
|
meillo@31
|
1053 .PP
|
|
meillo@31
|
1054 Apart from the user's perspective, \s-1MH\s0 is development-friendly.
|
|
meillo@31
|
1055 Its overall design follows clear rules.
|
|
meillo@31
|
1056 The single tools do only one job, thus they are easy to understand,
|
|
meillo@31
|
1057 easy to write, and good to maintain.
|
|
meillo@31
|
1058 They are all independent and do not interfere with the others.
|
|
meillo@31
|
1059 Automated testing of their function is a straight forward task.
|
|
meillo@31
|
1060 .PP
|
|
meillo@31
|
1061 It is sad, that \s-1MH\s0's differentness is its largest problem,
|
|
meillo@31
|
1062 as its differentness is also its largest advantage.
|
|
meillo@31
|
1063 Unfortunately, for most people their habits are stronger
|
|
meillo@31
|
1064 than the attraction of the clear design and the power, \s-1MH\s0 offers.
|
|
meillo@0
|
1065
|
|
meillo@8
|
1066
|
|
meillo@8
|
1067
|
|
meillo@48
|
1068 .H 1 "Case study: uzbl
|
|
meillo@32
|
1069 .LP
|
|
meillo@32
|
1070 The last chapter took a look on the \s-1MUA\s0 \s-1MH\s0,
|
|
meillo@45
|
1071 which is an old and established software.
|
|
meillo@45
|
1072 This chapter covers uzbl, a fresh new project.
|
|
meillo@45
|
1073 Uzbl is a web browser that adheres to the Unix Philosophy.
|
|
meillo@45
|
1074 Its name comes from the \fILolspeak\fP word for ``usable'';
|
|
meillo@45
|
1075 it is pronounced identical.
|
|
meillo@0
|
1076
|
|
meillo@48
|
1077 .H 2 "Historical background
|
|
meillo@0
|
1078 .LP
|
|
meillo@32
|
1079 Uzbl was started by Dieter Plaetinck in April 2009.
|
|
meillo@44
|
1080 The idea was born in a thread in the Arch Linux Forums.
|
|
meillo@32
|
1081 .[
|
|
meillo@44
|
1082 arch linux forums
|
|
meillo@44
|
1083 browser
|
|
meillo@32
|
1084 .]
|
|
meillo@32
|
1085 After some discussion about failures of well known web browsers,
|
|
meillo@32
|
1086 Plaetinck (alias Dieter@be) came up with a very sketchy proposal
|
|
meillo@32
|
1087 of how a better web browser could look like.
|
|
meillo@32
|
1088 To the question of another member, if Plaetinck would write that program,
|
|
meillo@32
|
1089 because it would sound fantastic, Plaetinck replied:
|
|
meillo@32
|
1090 ``Maybe, if I find the time ;-)''.
|
|
meillo@32
|
1091 .PP
|
|
meillo@32
|
1092 Fortunately, he found the time.
|
|
meillo@32
|
1093 One day later, the first prototype was out.
|
|
meillo@32
|
1094 One week later, uzbl had an own website.
|
|
meillo@47
|
1095 .[
|
|
meillo@47
|
1096 uzbl website
|
|
meillo@47
|
1097 .]
|
|
meillo@32
|
1098 One month after the first code showed up,
|
|
meillo@47
|
1099 a mailing list was installed to coordinate and discuss further development,
|
|
meillo@47
|
1100 and a wiki was added to store documentation and scripts that showed up on the
|
|
meillo@32
|
1101 mailing list and elsewhere.
|
|
meillo@32
|
1102 .PP
|
|
meillo@45
|
1103 In the, now, one year of uzbl's existence, it was heavily developed on various branches.
|
|
meillo@32
|
1104 Plaetinck's task became more and more to only merge the best code from the
|
|
meillo@32
|
1105 different branches into his main branch, and to apply patches.
|
|
meillo@47
|
1106 .[
|
|
meillo@47
|
1107 lwn uzbl
|
|
meillo@47
|
1108 .]
|
|
meillo@32
|
1109 About once a month, Plaetinck released a new version.
|
|
meillo@32
|
1110 In September 2009, he presented several forks of uzbl.
|
|
meillo@47
|
1111 .[ [
|
|
meillo@47
|
1112 uzbl website
|
|
meillo@47
|
1113 .], news archive]
|
|
meillo@38
|
1114 Uzbl, actually, opened the field for a whole family of web browsers with similar shape.
|
|
meillo@32
|
1115 .PP
|
|
meillo@32
|
1116 In July 2009, \fILinux Weekly News\fP published an interview with Plaetinck about uzbl.
|
|
meillo@47
|
1117 .[
|
|
meillo@47
|
1118 lwn uzbl
|
|
meillo@47
|
1119 .]
|
|
meillo@32
|
1120 In September 2009, the uzbl web browser was on \fISlashdot\fP.
|
|
meillo@47
|
1121 .[
|
|
meillo@47
|
1122 slashdot uzbl
|
|
meillo@47
|
1123 .]
|
|
meillo@0
|
1124
|
|
meillo@48
|
1125 .H 2 "Contrasts to other web browsers
|
|
meillo@0
|
1126 .LP
|
|
meillo@32
|
1127 Like most \s-1MUA\s0s are monolithic, but \s-1MH\s0 is a toolchest,
|
|
meillo@32
|
1128 most web browsers are monolithic, but uzbl is a frontend to a toolchest.
|
|
meillo@32
|
1129 .PP
|
|
meillo@32
|
1130 Today, uzbl is divided into uzbl-core and uzbl-browser.
|
|
meillo@32
|
1131 Uzbl-core is, how its name already indicates, the core of uzbl.
|
|
meillo@32
|
1132 It handles commands and events to interface other programs,
|
|
meillo@45
|
1133 and also displays webpages by using \fIwebkit\fP as render engine.
|
|
meillo@32
|
1134 Uzbl-browser combines uzbl-core with a bunch of handler scripts, a status bar,
|
|
meillo@32
|
1135 an event manager, yanking, pasting, page searching, zooming, and more stuff,
|
|
meillo@32
|
1136 to form a ``complete'' web browser.
|
|
meillo@32
|
1137 In the following text, the term ``uzbl'' usually stands for uzbl-browser,
|
|
meillo@32
|
1138 so uzbl-core is included.
|
|
meillo@32
|
1139 .PP
|
|
meillo@32
|
1140 Unlike most other web browsers, uzbl is mainly the mediator between the
|
|
meillo@45
|
1141 various tools that cover single jobs.
|
|
meillo@35
|
1142 Therefore, uzbl listens for commands on a named pipe (fifo), a Unix socket,
|
|
meillo@35
|
1143 and on stdin, and it writes events to a Unix socket and to stdout.
|
|
meillo@35
|
1144 Loading a webpage in a running uzbl instance requires only:
|
|
meillo@32
|
1145 .DS
|
|
meillo@32
|
1146 echo 'uri http://example.org' >/path/to/uzbl-fifo
|
|
meillo@32
|
1147 .DE
|
|
meillo@45
|
1148 The graphical rendering of the webpage is done by webkit,
|
|
meillo@45
|
1149 a web content engine.
|
|
meillo@45
|
1150 Uzbl-core is built around libwebkit.
|
|
meillo@32
|
1151 .PP
|
|
meillo@45
|
1152 Downloads, browsing history, bookmarks, and the like are not provided
|
|
meillo@45
|
1153 by the core itself, like they are in other web browsers.
|
|
meillo@35
|
1154 Uzbl-browser also only provides, so called, handler scripts that wrap
|
|
meillo@35
|
1155 external applications which provide the actual functionality.
|
|
meillo@32
|
1156 For instance, \fIwget\fP is used to download files and uzbl-browser
|
|
meillo@32
|
1157 includes a script that calls wget with appropriate options in
|
|
meillo@32
|
1158 a prepared environment.
|
|
meillo@32
|
1159 .PP
|
|
meillo@32
|
1160 Modern web browsers are proud to have addons, plugins, and modules, instead.
|
|
meillo@32
|
1161 This is their effort to achieve similar goals.
|
|
meillo@35
|
1162 But instead of using existing, external programs, modern web browsers
|
|
meillo@45
|
1163 include these functions.
|
|
meillo@0
|
1164
|
|
meillo@48
|
1165 .H 2 "Discussion of the design
|
|
meillo@0
|
1166 .LP
|
|
meillo@32
|
1167 This section discusses uzbl in regard of the Unix Philosophy,
|
|
meillo@32
|
1168 as identified by Gancarz.
|
|
meillo@32
|
1169
|
|
meillo@32
|
1170 .PP
|
|
meillo@35
|
1171 .B "Make each program do one thing well" .
|
|
meillo@35
|
1172 Uzbl tries to be a web browser and nothing else.
|
|
meillo@36
|
1173 The common definition of a web browser is, of course, highly influenced by
|
|
meillo@36
|
1174 existing implementations of web browsers, although they are degenerated.
|
|
meillo@35
|
1175 Web browsers should be programs to browse the web, and nothing more.
|
|
meillo@45
|
1176 This is the one thing they should do.
|
|
meillo@36
|
1177 .PP
|
|
meillo@45
|
1178 Web browsers should not, for instance, manage downloads.
|
|
meillo@35
|
1179 This is the job download managers exist for.
|
|
meillo@35
|
1180 Download managers do primary care about being good in downloading files.
|
|
meillo@35
|
1181 Modern web browsers provide download management only as a secondary feature.
|
|
meillo@45
|
1182 How could they do this job better, than programs that exist only for
|
|
meillo@35
|
1183 this very job?
|
|
meillo@35
|
1184 And how could anyone want less than the best download manager available?
|
|
meillo@32
|
1185 .PP
|
|
meillo@35
|
1186 A web browser's job is to let the user browse the web.
|
|
meillo@35
|
1187 This means, navigating through websites by following links.
|
|
meillo@36
|
1188 Rendering the \s-1HTML\s0 sources is a different job, too.
|
|
meillo@36
|
1189 It is covered by the webkit render engine, in uzbl's case.
|
|
meillo@35
|
1190 Audio and video content and files like PostScript, \s-1PDF\s0, and the like,
|
|
meillo@36
|
1191 are also not the job of a web browser.
|
|
meillo@36
|
1192 They should be handled by external applications \(en
|
|
meillo@36
|
1193 ones which's job is to handle such data.
|
|
meillo@35
|
1194 Uzbl strives to do it this way.
|
|
meillo@36
|
1195 .PP
|
|
meillo@36
|
1196 Remember Doug McIlroy:
|
|
meillo@35
|
1197 .I
|
|
meillo@35
|
1198 ``Write programs that do one thing and do it well.
|
|
meillo@35
|
1199 Write programs to work together.''
|
|
meillo@35
|
1200 .R
|
|
meillo@35
|
1201 .PP
|
|
meillo@35
|
1202 The lesser tenet
|
|
meillo@35
|
1203 .B "allow the user to tailor the environment
|
|
meillo@35
|
1204 matches good here.
|
|
meillo@35
|
1205 There was the question, how anyone could want anything less than the
|
|
meillo@35
|
1206 best program for the job.
|
|
meillo@45
|
1207 But as personal preferences matter, it is probably more important to ask:
|
|
meillo@35
|
1208 How could anyone want something else than his preferred program for the job?
|
|
meillo@36
|
1209 .PP
|
|
meillo@45
|
1210 Usually users want one program for a specific job.
|
|
meillo@35
|
1211 Hence, whenever the task is, for instance, downloading,
|
|
meillo@45
|
1212 the same download manager should be used.
|
|
meillo@35
|
1213 More advanced users might want to have this download manager in this
|
|
meillo@35
|
1214 situation and that one in that situation.
|
|
meillo@35
|
1215 They should be able to configure it this way.
|
|
meillo@35
|
1216 With uzbl, one can use any download manager the user wants.
|
|
meillo@36
|
1217 To switch to a different one, only one line in a small handler script
|
|
meillo@35
|
1218 needs to be changed.
|
|
meillo@45
|
1219 Alternatively it would be possible to query the program to use by
|
|
meillo@45
|
1220 reading a global file or an environment variable, in the handler script.
|
|
meillo@36
|
1221 .PP
|
|
meillo@45
|
1222 Uzbl does neither have its own download manager nor depends on a
|
|
meillo@45
|
1223 specific one, hence uzbl's browsing abilities will not be lowered by having
|
|
meillo@35
|
1224 a bad download manager.
|
|
meillo@45
|
1225 Uzbl's download capabilities will be just as good as the ones of the best
|
|
meillo@36
|
1226 download manager available on the system.
|
|
meillo@38
|
1227 Of course, this applies to all of the other supplementary tools, too.
|
|
meillo@32
|
1228
|
|
meillo@32
|
1229 .PP
|
|
meillo@36
|
1230 .B "Use software leverage to your advantage" .
|
|
meillo@36
|
1231 Uzbl is designed to be extended by external tools.
|
|
meillo@36
|
1232 These external tools are usually wrapped by small handler shell scripts.
|
|
meillo@36
|
1233 Shell scripts are the glue in this approach.
|
|
meillo@36
|
1234 They make the various parts fit together.
|
|
meillo@36
|
1235 .PP
|
|
meillo@45
|
1236 The history mechanism of uzbl shall be presented as an example.
|
|
meillo@36
|
1237 Uzbl is configured to spawn a script to append an entry to the history
|
|
meillo@36
|
1238 whenever the event of a fully loaded page occurs.
|
|
meillo@45
|
1239 The script to append the entry to the history is not much more than:
|
|
meillo@36
|
1240 .DS
|
|
meillo@36
|
1241 #!/bin/sh
|
|
meillo@36
|
1242 file=/path/to/uzbl-history
|
|
meillo@36
|
1243 echo `date +'%Y-%m-%d %H:%M:%S'`" $6 $7" >> $file
|
|
meillo@36
|
1244 .DE
|
|
meillo@36
|
1245 \f(CW$6\fP and \f(CW$7\fP expand to the \s-1URL\s0 and the page title.
|
|
meillo@45
|
1246 .PP
|
|
meillo@45
|
1247 For loading an entry, a key is bound to spawn a load-from-history script.
|
|
meillo@36
|
1248 The script reverses the history to have newer entries first,
|
|
meillo@45
|
1249 then displays \fIdmenu\fP to let the user select an item,
|
|
meillo@36
|
1250 and afterwards writes the selected \s-1URL\s0 into uzbl's command input pipe.
|
|
meillo@45
|
1251 With error checking and corner case handling removed,
|
|
meillo@45
|
1252 the script looks like this:
|
|
meillo@36
|
1253 .DS
|
|
meillo@36
|
1254 #!/bin/sh
|
|
meillo@36
|
1255 file=/path/to/uzbl-history
|
|
meillo@36
|
1256 goto=`tac $file | dmenu | cut -d' ' -f 3`
|
|
meillo@36
|
1257 echo "uri $goto" > $4
|
|
meillo@36
|
1258 .DE
|
|
meillo@36
|
1259 \f(CW$4\fP expands to the path of the command input pipe of the current
|
|
meillo@36
|
1260 uzbl instance.
|
|
meillo@32
|
1261
|
|
meillo@32
|
1262 .PP
|
|
meillo@33
|
1263 .B "Avoid captive user interfaces" .
|
|
meillo@36
|
1264 One could say, that uzbl, to a large extend, actually \fIis\fP
|
|
meillo@36
|
1265 a captive user interface.
|
|
meillo@37
|
1266 But the difference to most other web browsers is, that uzbl is only
|
|
meillo@45
|
1267 the captive user interface frontend (and the core of the backend).
|
|
meillo@38
|
1268 Many parts of the backend are independent of uzbl.
|
|
meillo@45
|
1269 Some are distributed with uzbl, for some external programs,
|
|
meillo@45
|
1270 handler scripts are distributed,
|
|
meillo@45
|
1271 but arbitrary additional functionality can be added if desired.
|
|
meillo@37
|
1272 .PP
|
|
meillo@37
|
1273 The frontend is captive \(en that is true.
|
|
meillo@37
|
1274 This is okay for the task of browsing the web, as this task is only relevant
|
|
meillo@37
|
1275 for humans.
|
|
meillo@37
|
1276 Automated programs would \fIcrawl\fP the web.
|
|
meillo@37
|
1277 That means, they read the source directly.
|
|
meillo@37
|
1278 The source includes all the semantics.
|
|
meillo@37
|
1279 The graphical representation is just for humans to transfer the semantics
|
|
meillo@37
|
1280 more intuitively.
|
|
meillo@32
|
1281
|
|
meillo@32
|
1282 .PP
|
|
meillo@33
|
1283 .B "Make every program a filter" .
|
|
meillo@37
|
1284 Graphical web browsers are almost dead ends in the chain of information flow.
|
|
meillo@37
|
1285 Thus it is difficult to see what graphical web browsers should filter.
|
|
meillo@45
|
1286 Graphical web browsers exist almost only to be interactively used by humans.
|
|
meillo@37
|
1287 The only case when one might want to automate the rendering function is
|
|
meillo@37
|
1288 to generate images of rendered webpages.
|
|
meillo@37
|
1289
|
|
meillo@37
|
1290 .PP
|
|
meillo@37
|
1291 .B "Small is beautiful"
|
|
meillo@45
|
1292 is not easy to apply to a web browser, because modern web technology
|
|
meillo@45
|
1293 is very complex, hence the rendering task is very complex.
|
|
meillo@45
|
1294 Modern web browsers have to consist of many thousand lines of code,
|
|
meillo@37
|
1295 unfortunately.
|
|
meillo@37
|
1296 Using the toolchest approach and wrappers can split the browser into
|
|
meillo@37
|
1297 several small parts, tough.
|
|
meillo@37
|
1298 .PP
|
|
meillo@45
|
1299 As of March 2010, uzbl-core consists of about 3\,500 lines of C code.
|
|
meillo@37
|
1300 The distribution includes another 3\,500 lines of Shell and Python code,
|
|
meillo@37
|
1301 which are the handler scripts and plugins like a modal interface.
|
|
meillo@38
|
1302 Further more, uzbl uses functionality of external tools like
|
|
meillo@38
|
1303 \fIwget\fP and \fInetcat\fP.
|
|
meillo@37
|
1304 Up to this point, uzbl looks pretty neat and small.
|
|
meillo@38
|
1305 The ugly part of uzbl is the web content renderer, webkit.
|
|
meillo@37
|
1306 Webkit consists of roughly 400\,000 (!) lines of code.
|
|
meillo@38
|
1307 Unfortunately, small web render engines are not possible anymore
|
|
meillo@38
|
1308 because of the modern web.
|
|
meillo@35
|
1309
|
|
meillo@35
|
1310 .PP
|
|
meillo@35
|
1311 .B "Build a prototype as soon as possible" .
|
|
meillo@35
|
1312 Plaetinck made his code public, right from the beginning.
|
|
meillo@38
|
1313 Discussion and development was, and still is, open to everyone interested.
|
|
meillo@38
|
1314 Development versions of uzbl can be obtained very simply from the code
|
|
meillo@38
|
1315 repository.
|
|
meillo@38
|
1316 Within the first year of uzbl's existence, a new version was released
|
|
meillo@35
|
1317 more often than once a month.
|
|
meillo@38
|
1318 Different forks and branches arose.
|
|
meillo@45
|
1319 They introduced new features, which were tested for suitability
|
|
meillo@45
|
1320 for the main branch.
|
|
meillo@35
|
1321 The experiences of using prototypes influenced further development.
|
|
meillo@35
|
1322 Actually, all development was community driven.
|
|
meillo@38
|
1323 Plaetinck says, three months after uzbl's birth:
|
|
meillo@35
|
1324 ``Right now I hardly code anything myself for Uzbl.
|
|
meillo@35
|
1325 I just merge in other people's code, ponder a lot, and lead the discussions.''
|
|
meillo@35
|
1326 .[
|
|
meillo@44
|
1327 lwn
|
|
meillo@44
|
1328 uzbl
|
|
meillo@35
|
1329 .]
|
|
meillo@32
|
1330
|
|
meillo@0
|
1331
|
|
meillo@48
|
1332 .H 2 "Problems
|
|
meillo@0
|
1333 .LP
|
|
meillo@38
|
1334 Similar to \s-1MH\s0, uzbl, too suffers from being different.
|
|
meillo@38
|
1335 It is sad, but people use what they know.
|
|
meillo@38
|
1336 Fortunately, uzbl's user interface can look and feel very much the
|
|
meillo@38
|
1337 same as the one of the well known web browsers,
|
|
meillo@38
|
1338 hiding the internal differences.
|
|
meillo@38
|
1339 But uzbl has to provide this similar look and feel to be accepted
|
|
meillo@38
|
1340 as a ``normal'' browser by ``normal'' users.
|
|
meillo@37
|
1341 .PP
|
|
meillo@45
|
1342 Though, the more important problem is the modern web.
|
|
meillo@38
|
1343 The modern web is simply broken.
|
|
meillo@38
|
1344 It has state in a state-less protocol,
|
|
meillo@38
|
1345 it misuses technologies,
|
|
meillo@38
|
1346 and it is helplessly overloaded.
|
|
meillo@38
|
1347 The result are web content render engines that must consist
|
|
meillo@38
|
1348 of hundreds of thousands lines of code.
|
|
meillo@38
|
1349 They also must combine and integrate many different technologies,
|
|
meillo@45
|
1350 only to make our modern web accessible.
|
|
meillo@38
|
1351 Website to image converter are hardly possible to run without
|
|
meillo@38
|
1352 human interaction because of state in sessions, impossible
|
|
meillo@38
|
1353 deep-linking, and unautomatable technologies.
|
|
meillo@37
|
1354 .PP
|
|
meillo@38
|
1355 The web was misused to provide all kinds of imaginable wishes.
|
|
meillo@38
|
1356 Now web browsers, and eventually the users, suffer from it.
|
|
meillo@37
|
1357
|
|
meillo@8
|
1358
|
|
meillo@48
|
1359 .H 2 "Summary uzbl
|
|
meillo@32
|
1360 .LP
|
|
meillo@38
|
1361 ``Uzbl is a browser that adheres to the Unix Philosophy'',
|
|
meillo@38
|
1362 that is how uzbl is seen by its authors.
|
|
meillo@38
|
1363 Indeed, uzbl follows the Unix Philosophy in many ways.
|
|
meillo@38
|
1364 It consists of independent parts that work together,
|
|
meillo@45
|
1365 while its core is mainly a mediator which glues the parts together.
|
|
meillo@38
|
1366 .PP
|
|
meillo@38
|
1367 Software leverage can excellently be seen in uzbl.
|
|
meillo@45
|
1368 External tools are used, independent tasks are separated
|
|
meillo@45
|
1369 in independent parts and glued together with small handler scripts.
|
|
meillo@38
|
1370 .PP
|
|
meillo@38
|
1371 As uzbl, more or less, consists of a set of tools and a bit
|
|
meillo@38
|
1372 of glue, anyone can put the parts together and expand it
|
|
meillo@38
|
1373 in any desired way.
|
|
meillo@38
|
1374 Uzbl is very flexible and customizable.
|
|
meillo@38
|
1375 These properties make it valuable for advanced users,
|
|
meillo@38
|
1376 but may keep novice users from using it.
|
|
meillo@38
|
1377 .PP
|
|
meillo@45
|
1378 But uzbl's main problem is the modern web, that makes it hard
|
|
meillo@38
|
1379 to design a sane web browser.
|
|
meillo@38
|
1380 Despite this bad situation, uzbl does a fairly good job.
|
|
meillo@32
|
1381
|
|
meillo@8
|
1382
|
|
meillo@48
|
1383 .H 1 "Final thoughts
|
|
meillo@0
|
1384
|
|
meillo@48
|
1385 .H 2 "Quick summary
|
|
meillo@0
|
1386 .LP
|
|
meillo@0
|
1387 good design
|
|
meillo@0
|
1388 .LP
|
|
meillo@0
|
1389 unix phil
|
|
meillo@0
|
1390 .LP
|
|
meillo@0
|
1391 case studies
|
|
meillo@0
|
1392
|
|
meillo@48
|
1393 .H 2 "Why people should choose
|
|
meillo@0
|
1394 .LP
|
|
meillo@0
|
1395 Make the right choice!
|
|
meillo@0
|
1396
|
|
meillo@47
|
1397
|
|
meillo@47
|
1398 .bp
|
|
meillo@47
|
1399 .TL
|
|
meillo@47
|
1400 References
|
|
meillo@47
|
1401 .LP
|
|
meillo@47
|
1402 .XS
|
|
meillo@47
|
1403 .sp .5v
|
|
meillo@47
|
1404 .B
|
|
meillo@47
|
1405 References
|
|
meillo@47
|
1406 .XE
|
|
meillo@47
|
1407 .ev r
|
|
meillo@42
|
1408 .nr PS -1
|
|
meillo@42
|
1409 .nr VS -1
|
|
meillo@0
|
1410 .[
|
|
meillo@0
|
1411 $LIST$
|
|
meillo@0
|
1412 .]
|
|
meillo@47
|
1413 .nr PS +1
|
|
meillo@47
|
1414 .nr VS +1
|
|
meillo@47
|
1415 .ev
|
|
meillo@47
|
1416
|
|
meillo@42
|
1417 .bp
|
|
meillo@47
|
1418 .TL
|
|
meillo@47
|
1419 Table of Contents
|
|
meillo@47
|
1420 .LP
|
|
meillo@47
|
1421 .PX no
|
